Optical information reproducing method and apparatus for performing reproduction compensation

ABSTRACT

The present invention provides an optical information reproducing method of detecting a record mark formed in an optical information recording medium and generating a reproduced signal, comprising the steps of: detecting a mark length of each record mark on basis of a reproduced signal, and correcting the reproduced signal by a correction amount corresponding to the detected mark length, and an optical information reproducing apparatus for detecting a record mark formed in an optical information recording medium and generating a reproduced signal, comprising: a detection circuit for detecting a mark length of each record mark on basis of a reproduced signal, and a correction circuit for correcting the reproduced signal by a correction amount corresponding to the detected mark length.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information reproducingmethod and an optical information reproducing apparatus which are usedfor optical information recording media such as a magneto-optical disk,a compact disk (CD), and a CD-R, and in particular, is suitable for anoptical magnetic reproducing method and an optical magnetic reproducingapparatus which reproduce information by utilizing aphoto-electro-magnetic effect.

2. Related Background Art

Up to now in a record/reproduction system by optical informationrecording media, such as a magneto-optical disk, a compact disk, and aCD-R, it is known that a waveform deviation arises in a recorded signalor a reproduced signal according to the characteristics of a medium. Theoutline of waveform deviation will be described referring to FIGS. 41Aand 41B. FIG. 41A shows a reproduced waveform and FIG. 41B shows decodeddata. Here, it is assumed that a reproduced waveform is sampled at aleading edge of a clock in a reproduction system. A mark “x” in FIG. 41Adenotes a sampling signal. If a waveform deviation arises due to thecharacteristics of a medium, a leading edge location is changed minutelydue to the waveform deviation shown by a broken line when a signalchanges from a level “H” to a level “L” at the time k1 in FIG. 41A. Whenthe reproduced waveform where the waveform deviation arises is sampled,it becomes a factor of degrading a PLL loop and a decoder that aresubsequent stages.

On the other hand, for example, Japanese Patent Application Laid-OpenNo. 10-50000 discloses a method of performing a data detectiondetermination after adding a predetermined positive offset value toreproduced data at a turning point where a level shift from the level“H” to the level “L”. In addition, Japanese Patent Application Laid-OpenNo. 05-197957 discloses a method of compensating a waveform deviation atthe time of recording by measuring record pulse width, etc. at the timeof information record, and controlling a leading edge location.

By the way, in a PLL loop (data PLL) based on the sampled data of areproduced signal, incorrect detection arises in a phase error signal bythe waveform deviation. FIG. 26 shows the outline of the phase errordetection in data PLL. In the data PLL, a phase error is obtained on thebasis of the sampled data in an edge section of a reproduced signal. InFIGS. 42A to 42D, numeral 920 denotes a reproduced signal, and a blackcircle “●” and an open circle “∘” are sampled data with a clock.

FIG. 42A shows a case where the phase of the clock delays from the phaseof the reproduced signal, and a phase error is outputted as a positivevalue. FIG. 42B shows a case where the phase of the clock is inconformity with the phase of the reproduced signal, and a phase errorbecomes zero. FIG. 42C shows a case where the phase of the clock leadsthe phase of the reproduced signal, and a phase error is outputted as anegative value. The PLL loop performs controls on the basis of thisphase error signal. However, if waveform deviation 930 to the reproducedsignal 920 arises as shown in FIG. 42D, a phase error detected in anedge section becomes a value shown by a black square “▪”, and an errorvalue is generated.

However, the above-described method of Japanese Patent ApplicationLaid-Open No. 10-50000 in which only a level changing point is referredcannot treat, for example, a case where an amount of a waveformdeviation changes depending on a waveform pattern to the changing point.Here, if a section of the level “H” is referred to as a mark, and asection of the level “L” is referred to as a space. If fluctuating theamount of a waveform deviation depending on an interval of the mark andspace, etc., it is not possible to obtain a desired effect unless acorrection amount of a waveform deviation is set adaptively according tothe interval (record mark length) of the mark or space.

Furthermore, the method of compensating a waveform deviation at the timeof record that is disclosed in Japanese Patent Application Laid-Open No.05-197957 has a large possibility of generating bit droppage, etc. bythe influence of compensation by a record pulse below the shortest marklength if the shortest mark length is shortened for a highdensification. In addition, since the edge section of a reproducedsignal is used in the data PLL, appropriate correction of the recordmark length becomes necessary for achieving desired performance.Therefore, correction by a fixed amount of correction at a changingpoint of a level that is disclosed in the above-described JapanesePatent Application Laid-Open No. 10-50000 could not treat the waveformdeviation of a reproduced signal.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedconventional problems, and an object of the present invention is toprovide an optical information reproducing method and an opticalinformation reproducing apparatus for correcting a waveform deviationgenerated by the characteristics of a medium, a record and reproductionsystem, etc., and for being able to correctly reproduce recordinginformation.

An example of achieving the object of the present invention is anoptical information reproducing method of detecting record marks formedin an optical information recording medium and generating a reproducedsignal, comprising the steps of;

detecting a mark length of each record mark based on a reproducedsignal; and

correcting the reproduced signal by a correction amount corresponding tothe detected mark length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a first embodiment of the presentinvention;

FIG. 2 is a block diagram showing the sequence of correction coefficientgeneration in FIG. 1;

FIG. 3 is a chart for explaining the binary conversion of a reproducedsignal;

FIGS. 4A, 4B and 4C are charts for explaining a jitter detection method;

FIG. 5 is a chart for explaining the relation between the jitter and themark length;

FIG. 6 is a block diagram for explaining the reproduction correctioncircuit in FIG. 1;

FIGS. 7A, 7B, 7C, 7D, 7E, 7F, 7G, 7H and 7I are timing charts forexplaining the operation of the first embodiment;

FIGS. 8A and 8B are diagrams for explaining a method of generation acorrection coefficient;

FIG. 9 is a diagram for explaining a waveform correction method;

FIG. 10 is a block diagram showing a second embodiment of the presentinvention;

FIGS. 11A, 11B and 11C are diagrams for explaining PR detection of marklength detection in FIG. 10;

FIGS. 12A, 12B and 12C are diagrams for explaining the outline of thejitter detection in FIG. 10;

FIGS. 13A and 13B are diagrams for explaining the outline of the jitterdetection in FIG. 10;

FIG. 14 is a diagram for explaining the generation of a correctionamount in FIG. 10;

FIG. 15 is a diagram for explaining the correction amount in FIG. 10;

FIG. 16 is a diagram for explaining the waveform correction in FIG. 10;

FIG. 17 is a block diagram showing a fourth embodiment of the presentinvention;

FIG. 18 is a diagram for explaining data PLL in FIG. 17;

FIG. 19 is a diagram for explaining user data in the present invention;

FIG. 20 is a diagram for explaining user data in the present invention;

FIG. 21 is a diagram for explaining a method of generating a correctioncoefficient;

FIG. 22 is a block diagram showing another configuration of the firstembodiment of a magneto-optical reproducing apparatus according to thepresent invention;

FIGS. 23A, 23B and 23C are diagrams showing an example of a reproducingmethod using a magnetic domain wall motion type magneto-optical medium;

FIGS. 24A, 24B and 24C are diagrams for explaining a stray magneticfield;

FIG. 25 is a block diagram showing a fifth embodiment of the presentinvention;

FIG. 26 is a block diagram showing a pattern detection circuit in FIG.25;

FIG. 27 is a chart for explaining the three-valued determination for adifferential signal;

FIG. 28 is a drawing for explaining the operation of pattern detection;

FIGS. 29A, 29B and 29C are diagrams for explaining the correctionprocessing of a waveform correction circuit in FIG. 25;

FIGS. 30A and 30B are diagrams for explaining a decoding method in FIG.25;

FIGS. 31A, 31B, 31C, 31D, 31E, 31F, 31G and 31H are timing charts forexplaining the operation of a fifth embodiment;

FIG. 32 is a block diagram showing a sixth embodiment of the presentinvention;

FIG. 33 is a block diagram showing a correction coefficient generationcircuit in FIG. 32;

FIG. 34 is a chart for explaining phase difference detection in FIG. 32;

FIGS. 35A, 35B, 35C and 35D are diagrams for explaining the operation ofthe correction coefficient generation circuit of FIG. 32;

FIG. 36 is a diagram for explaining the outline of the jitter detectionin FIG. 32;

FIG. 37 is a diagram for explaining the correction processing of awaveform correction circuit in FIG. 32;

FIG. 38 is a block diagram showing an eighth embodiment of the presentinvention;

FIG. 39 is a block diagram of data PLL in FIG. 38;

FIGS. 40A, 40B and 40C are diagrams for explaining a waveform deviationof a conventional reproduced signal;

FIGS. 41A and 41B are diagrams for explaining a waveform deviation of aconventional reproduced signal; and

FIGS. 42A, 42B, 42C and 42D are diagrams for explaining phase errordetection in the data PLL.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of the present invention will be describedreferring to the drawings. In addition, the present invention is usedfor an information reproducing method and an information reproducingapparatus for optical information recording media such as amagneto-optical disk, a compact disc, and a CD-R, and is not limited inparticular to an information reproducing method and an informationreproducing apparatus for magneto-optical recording media such as amagneto-optical disk. Nevertheless, hereafter, an informationreproducing method and an information reproducing apparatus for amagneto-optical recording medium for which the present invention is usedsuitably, and in particular, a magneto-optical disk will be described.In addition, in all the following embodiments, a mark portion and aspace portion of a signal are generically referred to as “record mark”.

Embodiment 1

FIG. 1 is a block diagram showing the configuration of a firstembodiment of a magneto-optical reproducing apparatus according to thepresent invention. In FIG. 1, numeral 101 denotes a magneto-optical diskas an information-recording medium, and numeral 102 denotes a spindlemotor for rotating the magneto-optical disk 101 at a predeterminedspeed. A magnetic head 103 for generating a magnetic field modulatedaccording to a record signal is arranged above the top face of themagneto-optical disk 101, and an optical head 104 is arranged below thebottom face of the disk with opposing the magnetic head 103.

The optical head 104 radiates a light beam for recording, and recordsinformation, or radiates the light beam for reproduction, detects thereflected light from the medium, and reproduces recorded information. Atthis time, a semiconductor laser (not shown in the drawings) that is alight source for recording and reproduction, and a photosensor (notshown in the drawings) that detects light reflected from a medium isprovided in the optical head 104. A semiconductor laser is driven by alaser drive circuit 108, and recording and reproduction of informationare performed by controlling a light beam of the semiconductor laser forrecording or reproduction. Moreover, as the magneto-optical disk 101, amagnetic domain wall motion-type magnet-optical medium is used, andinformation reproduction by magnetic domain wall motion is performed.

A reproducing method using this magnetic domain wall motion-typemagneto-optical medium is disclosed in, for example, Japanese PatentApplication Laid-Open No. 6-290496. An example of the reproducing methodusing the magnetic domain wall motion-type magneto-optical mediumdisclosed in this Japanese Patent Application Laid-Open No. 6-290496will be described with reference to FIGS. 23A to 23C.

FIGS. 23A to 23C are schematic diagrams for explaining the magneticdomain wall motion-type magneto-optical recording medium and an actionin a reproducing method thereof.

FIG. 23A is a schematic sectional view of a structural example of themagnetic domain wall motion-type magneto-optical recording medium. Themagnetic layers of this medium are formed by sequentially stacking afirst magnetic layer 11, a second magnetic layer 12, and a thirdmagnetic layer 13. An arrow 14 in each layer denotes the direction ofatomic spin. A magnetic domain wall 15 is formed in a boundary sectionof areas where directions of spins are mutually reverse. Moreover, arecord signal in this recording layer is also denoted as a graph at thebottom side of FIG. 23A. A first magnetic layer 11 comprises aperpendicular magnetic film having a relatively small magnetic domainwall coercive force and a large magnetic domain wall mobility at atemperature near the ambient temperature in comparison with a thirdmagnetic layer 13, a second magnetic layer 12 comprises a magnetic layerhaving a Curie temperature lower than the first magnetic layer 11 andthe third magnetic layer 13, and the third magnetic layer 13 is aperpendicular magnetic film.

FIG. 23B is a graph showing temperature distribution formed in theabove-described magneto-optical recording medium. Although thistemperature distribution may be induced on a medium by a light beamitself radiated for reproduction, it is desirable to raise temperatureahead a spot of the light beam for reproduction by using another heatingmeans together, and to form the temperature distribution having the peakof temperature behind the spot. Here, at a location x_(s), medium'stemperature becomes temperature T_(s) near the Curie temperature of thesecond magnetic layer 12.

FIG. 23C is a graph showing the distribution of the magnetic domain wallenergy density σ₁ of the first magnetic layer 11 corresponding to thetemperature distribution in FIG. 23B. If there is the inclination ofmagnetic domain wall energy density σ₁ in the direction x in thismanner, the force F₁ obtained from the following formula acts on amagnetic domain wall of each layer existing in the location x.F ₁=∂σ₁/∂_(x)

This force F₁ acts to move the magnetic domain wall to the side of alower magnetic domain wall energy. Since the first magnetic layer 11 ahas a small magnetic domain wall coercive force and a large magneticdomain wall mobility, a magnetic domain wall is independently moved bythis force F₁ with ease. However, since the medium's temperature islower than T_(s) in an area (a right-hand side in the figure) ahead ofthe location x_(s) and is in exchange coupling with the third magneticlayer 13 having a large magnetic domain wall coercive force, themagnetic domain wall in the first magnetic layer 11 is also fixed to thelocation corresponding to the location of the magnetic domain wall inthe third magnetic layer 13.

If the magnetic domain wall 15 is at the location x_(s) of a medium asshown in FIG. 23A, medium's temperature rises to the temperature T_(s)near the Curie temperature of the second magnetic layer, and theexchange coupling between the first magnetic layer and the thirdmagnetic layer is cut. Consequently, as a broken line arrow 17 shows,the magnetic domain wall 15 in the first magnetic layer momentarilymoves to an area where temperature is higher and magnetic domain wallenergy density is smaller.

When the magnetic domain wall 15 passes through the bottom of the spot16 of the light beam for reproduction, all the atomic spin of the firstmagnetic layer in the spot is aligned in one direction. Then, wheneverthe magnetic domain wall 15 comes to the location x_(s) with themovement of the medium, the magnetic domain wall 15 momentarily movesbelow the spot, the direction of the atomic spin in the spot isreversed, and all the spins are aligned in one direction. Consequently,as shown in FIG. 23A, the amplitude of a reproduced signal does notdepend on an interval (namely, record mark length) of the magneticdomain wall currently recorded, but always becomes a constant andgreatest amplitude, and hence, it is completely released from problemssuch as waveform interference resulting from the optical diffractionlimitation.

In the case of informational recording, the magneto-optical disc 101that is the above-described magnetic domain wall movement-typemagneto-optical medium is rotated at a predetermined rate by the spindlemotor 102, and record data is supplied to the pre-encoder 107 in thisstate. The pre-encoder 107, for example, performs the demodulation ofNRZI series of data. A modulated signal outputted from the pre-encoder107 is supplied to a magnetic head driver 106, and the magnetic headdriver 106 drives the magnetic head 103 for external magnetic fieldgeneration according to the modulated signal. Thereby, the magnetic head103 generates a magnetic field according to the modulated signal, andapplies it to the magneto-optical disk 101. Simultaneously, data isrecorded on the magneto-optical disk 101 by radiating a magneto-opticaldisk 101 with the light beam for recording generated from optical head104 by the driving signal from the laser drive circuit 108.

On the other hand, in the case of informational reproduction, similarly,the magneto-optical disk 101 is controlled to rotate at thepredetermined rate, and the light beam for reproduction is radiated onthe magneto-optical disk 101 from the optical head 104. The reflectedlight from the magneto-optical disk 101 is detected by a photosensor ofthe optical head 104, and an RF signal is generated. This RF signal issupplied to an AGC circuit 109 through a preamplifier 105, a gaincontrol is performed according to the RF signal in AGC circuit 109, andthe RF signal with a predetermined amplitude is generated.

The reproduced RF signal processed by the AGC circuit 109 is convertedinto a digital signal by an A/D converter 110 and A/D converter 120. TheRF digital signal converted into the digital signal is supplied to awaveform correction circuit 111 and a reproduction compensating circuit114. The reproduction compensating circuit 114 comprises a mark lengthdetection unit 115, a jitter detection unit 117 and a correction amountgeneration circuit 116 and detects the record mark length of data fromthe RF digital signal, and detects a jitter from the reproduced signalnear the rear edge at each mark length, and generates the waveformdeviation correction signal corresponding to each record mark length.The waveform correction circuit 111 corrects the RF digital signal basedon the waveform deviation correction signal supplied from thereproduction compensating circuit 114.

The corrected RF digital signal is outputted to a decoder circuit 112,and the decoder circuit 112 outputs decoded data by differentialdetection. In addition, here, although the decoded data is generated bythe differential detection, well-known decoding methods such as PRML anda bit-by-bit method can be used.

Next, the generation of a correction coefficient for reproductioncompensation that is the feature of this embodiment will be described.FIG. 2 shows the sequence of the generation of a correction coefficient.The feature of the present invention resides in that the correctioncoefficient for reproduction compensation is generated from user datathat a user reproduces and uses, and hence, it is not necessary torecord information especially for reproduction compensation.

At step S0 in FIG. 2, reproduction is started by the above-mentionedrecording and reproducing apparatus.

At step S1 in FIG. 2, a user data area is detected based on thereproduced signal, and the following processing is performed. FIG. 19 isa schematic diagram of a form of a reproduced signal. The reproducedsignal comprises a VFO where a signal at a single frequency is recorded,a SYNC which shows the start of a user data area, and user data. FIG. 20shows the detail of each unit. The VFO is recorded in a tone signal suchas a 4T pattern, and the SYNC is constituted with a unique pattern notappearing in a recorded code series such as 8T-7T. The mark lengthdetection unit 115 detects a SYNC pattern, and performs formationprocessing of the following correction coefficients.

First, as shown in FIGS. 42A to 42D, a clock signal whose phase cansample a zero cross point of a leading edge of the reproduced waveformis generated by the PLL circuit not shown in the drawings. The generatedclock is delayed by ½ clock phase, and is supplied to the A/D converter110. FIG. 41A shows the outline of a signal converted into the digitalsignal by the A/D converter 110. The mark “x” in FIG. 41A, as describedabove, denotes a sampling signal. The mark length detection unit 115performs the temporary determination of data by performing the binaryconversion in comparison with a threshold at step S2 in FIG. 2 from theabove-described reproduced signal. It is assumed that data isconstituted by two codes, “0” and “1”.

FIG. 3 shows the outline of binary conversion. The binary conversioncompares reproduced signal S(k) with a predetermined threshold (0), andperforms the temporary determination of data by the followings.S(k)<0→“0”S(k)≧0→“1”  (1)Here, although peak detection is used for detecting mark length, it isalso possible to use well-known detection methods such as thebelow-mentioned PR detection and PRML.

Next, at step S3 in FIG. 2, a mark length is obtained by counting thecontinuous number of “0” or “1” based on the temporary determinationresult.

In addition, the clock (which is not delayed by ½ clock phase) generatedby the above-mentioned PLL circuit is supplied to the above-mentionedA/D converter 120. Signal S′ sampled with this clock is supplied to ajitter detection unit 117.

The jitter of a reproduced signal is detected at step S4 in FIG. 2. Theoutline of the jitter detection is shown in FIGS. 4A to 4C. FIGS. 4A to4C show a reproduced signal 410 near a certain time, and a samplingsignal S′ (● and ∘). The jitter detection unit 117 measures a jitter bythe sampled data (∘) near the zero cross of S′. FIG. 4A shows the casewhere a leading edge shifts ahead, and the sampled data (∘) near thezero cross is shifted to the plus side. FIG. 4B shows the case where thephase of a leading edge coincides, FIG. 4C is the case where the leadingedge shifts behind, and hence, the sampled data (∘) near the zero crossis shifted to the minus side.

A jitter (J) is proportional to sampled data S′ (∘) near the zero cross,and can be generated by performing the multiplication of thepredetermined amplitude-time conversion factor m as follows:J=m·S′  (2)

As shown in FIG. 5, by the mark length detection unit 115 and the jitterdetection unit 117, the mark length n of a reproduced signal and thejitter J in the rear edge of this mark length can be obtained.

In the correction amount generation circuit 116, the correction amountof a reproduced signal is generated from the above-described mark lengthand jitter. An outline of the correction amount generation circuit 116is shown in FIG. 6.

Here, it is assumed that an RLL (1, 7) code is used as a recording code,and hence, the mark length of data after NRZI is restricted to 2 to 8.

As shown in FIG. 6, the correction amount generation circuit 116 has acounter counting the frequency of appearance in each mark length, and anadder adding a jitter in the rear edge section of each mark length,inside a data holding unit 601.

At step S5 in FIG. 2, the averages of jitters in each of theabove-described mark lengths are generated. In an averaging unit 602 inFIG. 6, a frequency of appearance in each mark length and an additionvalue of the jitter in each mark length are read from the data holdingunit 601 by a control signal from a CPU not shown in the drawings, andan average of the jitter in each mark length in its rear edge iscomputed. FIG. 8A shows the outline of the distribution of jitters incertain mark length.

The correction coefficient generation unit 603, as shown at step S6 inFIG. 2, calculates a reproduction compensation coefficient based on theaverage of jitters in each mark length. FIG. 8B is a graph obtained byplotting the mark length in a horizontal axis and the jitter average ina vertical axis. The correction coefficient generation unit 603 obtainsan approximation line with, for example, a method of least squares, onthe basis of the data shown in FIG. 8B. The approximation line shown inFIG. 8B is as follows:J=A·n+B  (3)Here, J denotes a jitter, n denotes a mark length, and A and B denotereproduction correction coefficients.

In addition, although the method for obtaining a jitter J by the linearapproximation shown in Formula (3) here is shown, it is possible toarbitrarily set a degree, etc. and to increase correction coefficientsaccording to the degree. In addition, it is good to performapproximation with well-known methods such as polynomial approximationas shown in FIG. 21. Furthermore, it is also effective to generate thecorrection amount by holding jitters in each mark length shown in FIG.8B in memory, etc. and reading them.

In the correction amount generation unit 604 in FIG. 6, as shown at stepS7 in FIG. 2, the correction amount for a reproduced signal isgenerated. The jitter J is generated by using the mark length n, whichis detected in the mark length determination unit 115 based on thereproduced signal, and the above-described correction coefficients A andB, and a correction amount Y is computed as follows:Y=J·r  (4)Here, r denotes a jitter amplitude conversion coefficient that isdetermined by characteristics of a medium, a record and reproductionsystem, etc.

As for the generation of the correction coefficient, in an initialstate, the information on the record mark lengths and jitters for thegeneration of the correction coefficient is accumulated by performingreproduction for predetermined time or reproduction of the predeterminedvolume of data, and the correction coefficient is computed by theabove-described processing. For example, the correction coefficient isgenerated based on a reproduced signal corresponding to several tens ofsectors after reproduction start, that is, about 75,000 to 150,000 bitsin a number of bits. Next, in a steady state, the correction coefficientis generated with serially updating the above-described record marklengths and jitters.

As the timing of update of the correction coefficient, it is alsopossible to update it every predetermined time interval besides seriallyupdating, and it is also possible to accumulate record mark lengths andjitters every predetermined time interval or every data amount, and toupdate the correction coefficient based on these data.

Here, in magneto-optical recording, the temperature of a laser beamirradiation section of a magneto-optical recording medium reaches to aCurie point by irradiation of a laser beam at the time of recording, andmagnetization disappears. However, at the peripheral section wheretemperature is not rising to a Curie point, magnetization exists and astray magnetic field caused by the magnetization exists. Although amagnetic domain wall which is a record mark edge is formed in a rearedge in the light beam traveling direction, those stray magnetic fieldsact in the state that they are superimposed on the modulation magneticfield applied by the magnetic head from the outside for magnetic domainwall formation, at the time of the magnetic domain wall formation whichis a record mark edge. The size of this stray magnetic field changeswith the interval between a magnetic domain wall formed immediatelybefore and a magnetic domain wall which is going to be formed next,i.e., the record mark length to be formed, and the mark length locatedin front of it. Therefore, the intensity of a stray magnetic field thatacts on a magnetic domain wall forming section changes with mark length(alternatively mark length row) to be recorded.

Hereafter, the above-described stray magnetic field will be explained.FIG. 24C is a diagram showing magnetization and a stray magnetic fieldcaused by it. Although a magnetic domain wall which is a record markedge is formed in a rear edge in the light beam traveling direction asshown in FIG. 24C, stray magnetic fields are superimposed on amodulation magnetic field applied by the magnetic head from the outsidefor magnetic domain wall formation.

The size of this stray magnetic field changes with the interval betweena magnetic domain wall formed immediately before and a magnetic domainwall which is going to be formed next, i.e., the record mark length tobe formed, and the mark length located in front of it. In addition, theformed location of a magnetic domain wall is determined in the relationbetween temperature and magnetic field strength. Here, since laser beamintensity and the application magnetic field strength from the magnetichead are kept in a steady state and the stray magnetic field intensitythat is superimposed differs if record mark length or a record marklength row differs, the magnetic field strength applied to a location ofmagnetic domain formation is an intensity obtained by superimposingstray magnetic field intensity on the magnetic field strength from themagnetic head. Hence, as described above, the magnetic field strengthsubstantially applied to a magnetic domain forming part changes with therecord mark length or record mark length row to be formed. Inconsequence, a phenomenon that a location of magnetic domain wallformation changes with record mark length appears.

Additional explanation will be performed by using FIGS. 24A to 24C. FIG.24A shows the case where the longest and shortest record marks amongrecorded codes are sequentially formed, and FIG. 24B shows the casewhere the shortest and longest record marks among recorded codes aresequentially formed. In FIGS. 24A to 24C, reference numeral 1 denotes alight beam, an arrow 2 shows a magnetization state of a recording layerof a magneto-optical recording medium, an arrow 3 shows the strength anddirection of an applied magnetic field from the magnetic head, and anarrow 4 shows the strength and direction of a stray magnetic field bythe magnetization state just before the formation of a magnetic domainwall. An arrow 5 shows the strength and direction of a stray magneticfield from the record mark located further ahead.

Here, according to the characteristics of a magneto-optical recordingmedium, the stray magnetic field in the direction shown by the arrow 4is applied in the direction in which the applied magnetic field from themagnetic head is increased at the time of magnetic domain wallformation, and the stray magnetic field in the direction shown by thearrow 5 is applied in the direction in which the applied magnetic fieldfrom the magnetic head is decreased at the time of magnetic domain wallformation.

Hence, sums of the applied magnetic fields shown by the arrows 3 to 5 inthe magnetic domain wall forming part differ in the cases in FIGS. 24Aand 24B, and larger magnetic field strength is applied to a recordinglayer in the case in FIG. 24B. In consequence, the location of magneticdomain wall formation is shifted by ΔA from a certain reference locationin the case in FIG. 24A and is shifted by ΔB in the case in FIG. 24B,and the relation between ΔA and ΔB results in ΔA<ΔB.

Furthermore, record mark length becomes small by adopting amagneto-optical recording and reproduction method, which can eliminaterestrictions of resolution of an optical system and can drasticallyimprove track recording density, such as a magnetic domain wallmovement-type magneto-optical medium. (1) Therefore, since themagnetization state in a certain range from the location of magneticdomain wall formation is further complicatedly changed and the straymagnetic field is also complicated, the edge shift by record mark lengthbecomes complicated. (2) Since a ratio of the edge shift amount, whichis caused by the above-described factor, to the mark length becomeslarge by record track density increasing and mark length becoming short,an edge shift problem by the stray magnetic field is manifested. (3)Since restrictions of the edge shift by inter-code interference causedby restrictions of resolution of an optical system is eliminated, theedge shift problem by the stray magnetic field is manifested.

In this embodiment, a waveform deviation occurring depending on recordmark length on the basis of such a phenomenon is corrected. That is, asshown in Formula (3), a correction amount is computed from the presentrecord mark length and a predetermined correction coefficient at thetime of information reproduction, and the waveform deviation of areproduced signal is corrected on the basis of this correction amount.

The waveform correction circuit 111 delays an RF digital signal suppliedfrom the A/D converter 110, and corrects the RF digital signal on thebasis of the correction amount Y, obtained from the correction amountgeneration circuit 116, and a signal F showing the direction of achange.

The outline of the correction is shown in FIG. 9. (A) of FIG. 9 shows awaveform of a reproduced signal, and each black circle ● shows asampling point. In addition, a broken line in (A) of FIG. 9 is awaveform after correction, and each asterisk * shows a sampling pointafter the correction. (B) of FIG. 9 shows sampled values beforecorrection and a binary-converted threshold, and (C) of FIG. 9 showssampled valued after the correction and the binary-converted threshold.Although level determination at an identification point 501 is difficultand it becomes easy to generate an error in the case in (B) FIG. 9, asshown in (C) of FIG. 9, it becomes possible to increase the accuracy ofthe level determination by performing correction.

The waveform correction circuit 111 adds the correction amount Y to thesampled data near a changing point on the basis of the change directionF of the reproduced signal supplied from the correction amountgeneration circuit 116, when the change direction F is “1” (leading edgeof the reproduced signal). In addition, when the change direction F is“0” (trailing edge of the reproduced signal), the sign of the correctionamount Y is reversed, and it is added to the sampled data near thechanging point.

The corrected RF digital signal is supplied to a decoder circuit 112.Here, the decoder circuit 112 performs decoding by binary conversionshown in FIG. 3.

As shown in FIG. 9, a decoding error due to a waveform deviation can bereduced by correcting a reproduced signal according to the mark length.

Next, the specific reproduction operation of this embodiment will beexplained on the basis of FIGS. 7A to 7I. FIG. 7A shows an RF digitalsignal, FIG. 7B shows a clock, FIG. 7C shows temporary determinationdata, FIG. 7D shows a mark length, FIG. 7E shows a jitter, FIG. 7F showschange direction, FIG. 7G shows a gate which sets a correction zone,FIG. 7H shows the amount of correction offsets, and FIG. 7I shows adigital signal after correction.

Here, when a light beam for reproduction is radiated from the opticalhead 104 onto the magneto-optical disk 101 which is rotating, thereflected light from the magneto-optical disk 101 is detected by theoptical head 104 and a reproduced signal is generated, and thereproduced signal is supplied to the A/D converter 110 through apreamplifier 105 and an AGC circuit 109. The A/D converter 110, as shownin FIG. 7A, outputs an RF digital signal with synchronizing with theclock in FIG. 7B, and supplies the RF digital signal to the mark lengthdetection unit 115.

The mark length detection unit 115 generates temporary determinationdata as shown in FIG. 7C, and simultaneously computes the record marklength n on the basis of the counter not shown in the drawings, etc.Furthermore, the mark length detection unit 115 detects the changedirection of leading and trailing edges from the temporary determinationdata in FIG. 7C, and outputs 1→0 as the change direction of thetemporary determination data 1→0 or outputs 0→1 as the change directionof the temporary determination data 0→1, as shown in FIG. 7F.

In addition, an RF digital signal not shown in the drawings which isshifted by ½ clock phase to RF digital signal in FIG. 7A is supplied tothe jitter detection unit 117. The jitter detection unit 117 detects ajitter in a rear edge of each mark from the RF digital signal whosephase is shifted, as shown in FIG. 7E. In addition, suffixes (k+1),(k+2), and the like given to the data in FIGS. 7A to 7I denote the dataof the (k+1)th mark, (k+2)th mark, and the like, respectively. Hence,for example, the mark length n(k+1) in FIG. 7D denotes that it is themark length corresponding to the mark M(k+1) of the RF digital signal inFIG. 7A.

The correction amount generation circuit 116 computes an average jitterevery mark length on the basis of record mark length n in FIG. 7D andjitters in FIG. 7E, and further computes correction coefficients A and Bin Formula (3). Next, a correction amount is computed by Formula (3),which is converted into the amplitude offset amount Y, and the offsetamount Y shown in FIG. 7H is outputted.

The waveform correction circuit 111 gives predetermined delay to the RFdigital signal obtained from the A/D converter 110, generates acorrection gate, which controls a zone where the RF digital signal iscorrected on the basis of a signal from the correction amount generationcircuit 116 as shown in FIG. 7G inside, and adds or subtracts an offsetto or from the amplitude of the RF digital signal in this correctiongate zone. That is, with corresponding to an edge section of the RFdigital signal, the correction gate signal in FIG. 7G is generated, andan offset is subtracted or added in the zone of “1” of this correctiongate signal. Therefore, since the reproduced signal shown by a brokenline in FIG. 7I is corrected into the reproduced signal shown by a solidline, the waveform deviation can be corrected.

In the apparatus according to this embodiment, since it generates acorrection coefficient for reproduction compensation on the basis ofuser data that is reproduced, an optimal correction coefficient for areproduced signal can be obtained. In addition, it is not necessary torecord beforehand a special pattern for the reproduction compensationfor using the user data, etc.

Furthermore, since the above-described correction coefficient isserially updated by the reproduction compensating circuit, it becomespossible to realize always optimal correction also to variation in time.

In addition, although jitters corresponding to all the mark lengths 2 to8 generated in RLL (1, 7) code are held and a correction coefficient isobtained in the above-described embodiment, as a simplified method, itis also effective to obtain a correction amount in each mark length bylinear approximation based on specific record mark lengths, for example,2, 4, and 8 of jitters.

In the embodiment described above, the jitter (J) every mark length isobtained on the basis of the sampled data near the zero cross, anaverage of jitters every mark length is further calculated, correctioncoefficients A and B are computed on the basis of this average, a jitterJ is generated by using the mark length n and the correctioncoefficients A and B, and the correction amount Y in the amplitudedirection is computed. Alternatively, it is possible to obtain a samplevalue near the zero cross every mark length, obtain an average value forthis sample value every mark length, calculate correction coefficientbased on this average value, and calculate correction amount in anamplitude direction. FIG. 22 is a block diagram showing anotherconfiguration of the first embodiment of a magneto-optical reproducingapparatus according to the present invention. As shown in FIG. 22, thisapparatus comprises: an amplitude displacement detection unit 717 whichdetects sampled data (open circles ◯ in FIGS. 4A to 4C) near a zerocross as shown in FIGS. 4A to 4C as amplitude displacement; a dataholding unit 801 which has a counter counting a frequency of appearanceevery mark length, and an adder adding amplitude in a rear edge sectionof each mark length, inside; an averaging unit 802 which calculates anaverage of amplitude every mark length; a correction coefficientgeneration unit 803 which computes a correction coefficient based onthis average; and a correction amount generation unit 804 which computesthe correction amount Y in the amplitude direction with respect to themark length by using the mark length and correction coefficient.

Embodiment 2

Next, a second embodiment of the present invention will be explained.The second embodiment is characterized in the generation of a correctioncoefficient, the generation method of a correction amount, and acorrection method in comparison with the above-mentioned embodiment.

FIG. 10 is a block diagram showing a second embodiment of the presentinvention, and therein, the explanation of the same portions as those inFIG. 1 will be omitted with assigning the same numerals as those havingthe same configuration and performing the same operation.

A mark length detection unit 130 in FIG. 10 temporarily determines areproduced signal that is sampled by PR detection. A jitter detectionunit 131 performs PR (1, −1) processing of a sampled RF digital signalS, and detects a jitter in an edge section. A correction amountgeneration circuit 132 generates a correction amount of a reproducedsignal based on the mark length and jitter. A waveform correctioncircuit 133 corrects sampled data near an edge of the RF digital signalS that is converted into a digital signal by the A/D converter 110. Adecoder circuit 134 decodes data by PR detection based on the RF digitalsignal that is corrected. In addition, it is not necessary to say that awell-known method such as a binary conversion, or PRML can be used as adecoding method. Hereafter, the detail of each part will be described.

The mark length detection unit 130 serially performs the processing ofsubtracting sampled data S(k−1) at one previous time unit from sampleddata S(k) at the present time unit with respect to the RF digital signalS. This processing is referred to as PR(1, −1) hereinafter. FIGS. 11A to11C is the outline of PR(1,−1). FIG. 11A shows sampled data of an RFdigital signal, FIG. 11B shows sampled data after PR(1, −1), and FIG.11C shows data after temporary determination. As shown in FIG. 11B,sampled data other than that in an edge section becomes approximatelyzero by PR(1, −1), and there is a characteristic that a low-frequencyvariable component is removable. Positive and negative thresholds±E isset in FIG. 11B, and under the following conditions temporarydetermination will be performed. In addition, sampled data after PR(1,−1) is referred to as Sd.Sd>+E→1Sd<−E→0Except the above, the determination result at one previous time unit isheld.

Temporary determination result is shown in FIG. 11C. A sampled data rowin FIG. 11C is set to be “11110” as a result of the temporarydetermination. At this time, the mark length is detected by counting thenumber of continuous codes “1” or “0” by a counter, etc.

The Jitter detection unit 131 performs PR(1, −1) similarly to the abovewith respect to an RF digital signal. FIG. 12A shows the RF digitalsignal digitized by the A/D converter 110, FIG. 12B shows sampled dataSd after PR(1, −1), and FIG. 12C shows a phase error Sp in an edgesection.

The jitter detection unit 131 sets a predetermined threshold withrespect to the sampled data row Sd, and compares each sampled data Sdwith the threshold. When the sampled data is larger than the threshold,it is determined that it is a leading edge section, and when the sampleddata is smaller than the threshold, it is determined that it is atrailing edge section. A phase error Sp is generated on the basis of thesampled data Sd near the edge which is determined, as follows.Sp(k)=Sd(k−2)−Sd(k)  (5)

Formula (5) expresses the difference between two points that sandwichthe peak of the sampled data after PR(1, −1). When the phase coincideswith that of the clock, Sp becomes zero, and Sp becomes negative whenthe phase advances, and becomes positive when the phase is delayed.

For example, as shown in FIG. 13A, an open circle ∘ denotes the samplingvalue S of a reproduced signal at the time of the phase coinciding withthat of the clock, and an open triangle Δ denotes the sampling value S′of the reproduced signal at the time of the phase being delayed. Apredetermined threshold is set with respect to the sampled data row Sd(shown by a black circle ●) and Sd′ (shown by a black triangle ▴) afterPR(1, −1), and comparison of each sampled data Sd and Sd′ with thethreshold is performed. When the sampled data Sd and Sd′ are larger thanthe threshold, it is determined that it is a leading edge section, andhere, Sd(k+1) and Sd(k+1)′ are determined as a leading edge section. Asshown in FIG. 13B, Sp(k+2)=Sd(k)−Sd(k+2)=0 when the phases of thereproduced signal and clock is in agreement, andSp(k+2)′=Sd(k)′−Sd(k+2)′>0 when the phase of the reproduced signal isdelayed from that of the clock.

The phase error Sp(k+2) in FIG. 12C is a phase error obtained by twopoints which sandwich a peak Sd(k+1) of PR(1, −1), and the phase errorSp(k+6) is a phase error obtained by two points which sandwich a peakSd(k+5). However, a sign of the phase error Sp obtained in a trailingedge section (when the above-mentioned peak value is negative) isreversed. Owing to this, as shown in FIG. 12C, it is possible to obtainphase error information in an edge section.

The jitter detection unit 131 converts the above-mentioned phase errorinformation into the jitter J in a time-axis with the phase error-jitterconversion coefficient h obtained from a medium's characteristics or thecharacteristics of a record and reproduction system with respect to thephase error information as follows.J=h·Sp  (6)

Next, a correction amount generation circuit 132 will be described. Thecorrection amount generation circuit 132 receives the information on amark length and a jitter from the mark length detection unit 130 and thejitter detection unit 131.

In this embodiment, data for reproduction compensation is held by makingthe kth and (k+1)th mark lengths and a jitter at a rear edge of the(k+1)th mark be a set.

FIG. 14 shows the relation between the mark lengths detected in the marklength detection unit 130 and the jitter detected in the jitterdetection unit 131 with respect to the reproduced signal. J82 in thejitter information in FIG. 14 shows a jitter in a rear edge of a 2T markin the combination of mark lengths 8T-2T in the reproduced signal.

The correction amount generation circuit 132 computes an average ofjitters every combination of the kth and (k+1)th mark lengths, and holdsit on the table shown in FIG. 15.

As update timing of a correction coefficient, in this embodiment, thecorrection coefficient is updated every logical data class (file unitetc.), or every class based on identification information (record time,date, etc.).

Next, the waveform correction of a reproduced signal will be described.

An RF digital signal digitized by the A/D converter 110 is supplied tothe mark length detection unit 130. The mark length detection unit 130detects the mark length from the sampled value of an RF digital signalas described above. Two detected mark lengths that are adjacent aresupplied to the correction amount generation circuit 132. The correctionamount generation circuit 132 calls a Jitter Jij (i: kth mark length, j:(k+1)th mark length) from the table shown in FIG. 15 based on two marklengths, and supplies it to the waveform correction circuit 133.

As shown in FIG. 16, the waveform correction circuit 133 computessampled data E2′ and E3′ that are corrected by linear interpolation fromsampled data E1 to E3 and an interpolation coefficient G (=−J) in anedge section (shown by black squares ▪). For example, E2′ can beobtained by the following Formula (4).From (E2′−E2)/(E1−E2)=G/T,E2′=(G/T)·E1+((T−G)/T)×E2  (7)

T denotes an interval between sampling clocks. In addition, although thecase of linear interpolation is shown here, it is also possible to useanother well-known interpolation method. Thereby, since the edge shiftby a waveform deviation can be reduced, it becomes possible to eliminatea factor of a decoding error and to aim at improvement in recordingdensity.

In this embodiment, since a signal after PR(1, −1) processing is usedfor the detection of the above-described jitter, the A/D converter forjitter detection in the first embodiment becomes unnecessary. Inaddition, even if a low frequency component of a reproduced signalfluctuates with cross talk under the influence of a record signal in anadjoining track, it is possible to perform stable reproductionprocessing since the low frequency component is suppressed by PR(1, −1).

Embodiment 3

Next, a third embodiment of the present invention will be explained.This embodiment is different from the second embodiment in a generationmethod of a correction amount in the correction amount generationcircuit 132 in FIG. 10.

As described above, the size of a stray magnetic field changes with aninterval between a magnetic domain wall formed immediately before and amagnetic domain wall which is going to be formed next, i.e., the recordmark length to be formed, and the mark length located in front of it.Hence, the edge shift by a waveform deviation is influenced by therecord mark length that is going to be formed, and the mark lengthlocated ahead of it.

Then, a correction amount J is generated with the following formula fromthe kth and (k+1)th mark lengths.J=−A·n(k)+B×n(k+1)  (8)Here, n(k) is the kth mark length, and n(k+1) is the (k+1)th marklength.

Coefficients A and B in Formula (8) are computed by a method of leastsquares, etc. on the basis of collected sampled data by holding thesampled data every combination of adjacent mark lengths in FIG. 15.Therefore, in this embodiment, a table where the coefficients A and Bare held is generated instead of the jitter J in each cell in FIG. 15.

A method of waveform correction, which is the same as that in the secondembodiment, detects the adjoining mark lengths, and calls theabove-mentioned coefficients A and B from the table, and computes acorrection amount with Formula (8). Hereafter, by correcting a waveformby the interpolation in the direction of a time-axis, it becomespossible to reduce the edge shift by the waveform deviation.

In addition, it is possible to simplify the structure of a system bymaking the coefficients A and B equal to each other, i.e. A=B as thesimplification of Formula (8). When the difference of the coefficients Aand B is minute, simplification with this method is effective.Furthermore, it is also possible to simplify Formula (8) by generating acorrection amount by using the mark length n(k+1) in present time bymaking the coefficient A zero. It becomes unnecessary to hold the marklength ahead of it.

Embodiment 4

Next, a fourth embodiment of the present invention will be explained.FIG. 17 is a block diagram showing the fourth embodiment of the presentinvention. In FIG. 17, a data PLL 154 is added to the structure inFIG. 1. Others are similar to those in FIG. 1. The data PLL 154generates a clock signal based on the reproduced signal by which awaveform deviation is corrected in the waveform correction circuit 111by the same method as that in the first embodiment.

FIG. 18 is a block diagram showing the configuration of the data PLL154. In this figure, a phase error detection unit 301 detects a phaseerror based on sampled data in a leading edge section of a reproducedsignal. A loop filter 302 performs removal of unnecessary noise from andreduction compensation of a phase error signal. A VCO 303 generates aclock signal with a frequency corresponding to a control voltage. Thedata PLL detects a phase error from the edge section of a reproducedsignal and supplies the detected signal as a control signal of the VCOafter filtering. By making this a loop, it is possible to obtain theclock synchronizing with the reproduced signal.

In the apparatus of this embodiment, since a phase error is detectedfrom the reproduced signal which corrects waveform deviation, theinfluence of incorrect detection as shown in FIG. 42D can be reduced,and a proper reproduced signal can be obtained. Owing to this, it ispossible to suppress out-of-locking by an error signal, etc. in a PLLloop, and to stabilize operation since the variation of the clock by anerror is decreased. In addition, a detection method of a phase error isnot limited to the above-described method, but another well-knowntechnology can be used.

Furthermore, in this embodiment, a form of a recording medium is notlimited to the form of a disk, but it may be, for example, a card. Inthis case, a record mark is arranged in a line, and information can bereproduced by linearly moving the card and the reproducing headrelatively.

Embodiment 5

FIG. 25 is a block diagram showing the configuration of a fifthembodiment of a magneto-optical reproducing apparatus according to thepresent invention. In FIG. 25, a magneto-optical disk 1101 is aninformation recording medium, and a spindle motor 1102 rotates themagneto-optical disk 1101 at a predetermined speed. A magnetic head 1103for generating a magnetic field modulated according to a record signalis arranged above the top face of the magneto-optical disk 1101, and anoptical head 1104 is arranged with opposing the magnetic head 1103 belowthe bottom face the disk.

The optical head 1104 radiates a light beam for recording, and recordsinformation, or radiates the light beam for reproduction, detects thereflected light from the medium, and reproduces recorded information. Atthis time, a semiconductor laser (not shown in the drawings) that is alight source for recording and reproduction, and a photosensor (notshown in the drawings) that detects light reflected from a medium isprovided in the optical head 1104. The semiconductor laser is driven bylaser drive circuit 1108, and recording and reproduction of informationare performed by controlling a light beam of the semiconductor laser forrecording or reproduction. Moreover, as the magneto-optical disk 1101, amagnetic domain wall motion-type magnet-optical medium is used, andinformation reproduction by magnetic domain wall motion is performed.

In the case of informational recording, the magneto-optical disk 1101 isrotated at a predetermined rate by the spindle motor 1102, and recordingdata is supplied to the pre-encoder 1107 in this state.

In the pre-encoder 1107, for example, an NRZI series of data modulationis performed. A modulated signal outputted from the pre-encoder 1107 issupplied to a magnetic head driver 1106, and the magnetic head driver1106 drives the magnetic head 1103 for external magnetic fieldgeneration according to the modulated signal. Thereby, the magnetic head1103 generates a magnetic field according to the modulated signal, andapplies it to the magneto-optical disk 1101. Simultaneously, data isrecorded on the magneto-optical disk 1101 by radiating themagneto-optical disk 1101 with the light beam for recording from opticalhead 1104 by the driving signal from the laser drive circuit 1108.

On the other hand, in the case of informational reproduction, similarly,the magneto-optical disk 1101 is controlled to rotate at thepredetermined rate, and the light beam for reproduction is radiated onthe magneto-optical disk 1101 from the optical head 1104. The reflectedlight from the magneto-optical disk 1101 is detected by a photosensor ofthe optical head 1104, and an RF signal is generated. This RF signal issupplied to the AGC circuit 1109 through the preamplifier 1105, the AGCcircuit 1109 performs gain control according to the RF signal togenerate an RF signal with a predetermined amplitude.

The reproduced RF signal processed by the AGC circuit 1109 is convertedinto a digital signal by the A/D converter 1110.

The RF digital signal converted into the digital signal is supplied to awaveform correction circuit 1111 and a reproduction compensating circuit1114. The reproduction compensating circuit 1114 comprises a mark lengthdetection circuit 1115 and a correction amount generation circuit 1116,detects the record mark length of data from the RF digital signal, andgenerates a waveform deviation correction signal corresponding to eachrecord mark length. The waveform correction circuit 1111 corrects the RFdigital signal based on the waveform deviation correction signalsupplied from the reproduction compensating circuit 1114.

The corrected RF digital signal is outputted to a decoder circuit 1112,and the decoder circuit 1112 outputs decoded data by differentialdetection. In addition, here, although the decoded data is generated bythe differential detection, well-known decoding methods such as PRML anda bit-by-bit method can be used.

Next, the operation of reproduction compensation of a waveform deviationthat is a characteristic of this embodiment will be described. Thereproduction compensating circuit 1114 comprises a mark length detectioncircuit 1115 and a correction amount generation circuit 1116. Theconfiguration of the mark length detection circuit 1115 is shown in FIG.26. In FIG. 26, a finite difference circuit 1201 outputs a differentialvalue of the RF digital signal. A mark length measurement circuit 1202measures an interval of a mark and a space as record mark length. Itsoperation will be described with referring to FIGS. 40A to 40C.

First, it is assumed that a reproduced waveform is, for example, asignal as shown in FIG. 40A. This is sampled with the clock generated bythe PLL circuit not shown in the drawings, and is supplied from A/Dconverter 1110 as a discrete digital signal. A mark “x” in FIG. 40A, asdescribed above, denotes a sampling signal. A differential circuit 1201generates a differential signal from the RF digital signal supplied fromthe A/D converter 1110. This differential signal is obtained bysubtracting a signal value, sampled before one time unit, from a currentsampled signal value, and, the generated differential signal has asignal waveform shown in FIG. 40C.

A differential signal generated by the differential circuit 1201 issupplied to the mark length measurement circuit 1202, and the marklength measurement circuit 1202 performs three-valued determination withrespect to the differential signal. Specifically, as shown in FIG. 27,positive and negative thresholds T1 and T2 are set to the differentialsignal d(k), and determination is performed by the following method.d(k)≧T1→“1”d(k)≦T2→“−1”

Other than the above →“0”

In the mark length measurement circuit 1202, three-valued determinationof a differential signal is performed by the above-described method,and, in the section where determination result is “0”, a counter valueof an internal counter is incremented with synchronizing with a clock(which is a clock generated by the PLL loop). Since a leading edge or atrailing edge of a reproduced signal is detected when determinationresult changes to “0” from “1” or “−1”, a counter value at that time isoutputted. Record mark length P becomes a value obtained by adding +1 tothe outputted counter value. The mark length measurement circuit 1202performs the measurement of the record mark length in this way, resetsthe counter after outputting the record mark length, and measures thenext record mark length.

In addition, assuming that a signal expressing the direction of a changeof a leading edge or a trailing edge is F, the mark length detectioncircuit 1115 outputs “F=1” to the correction amount generation circuit1116 as a leading section when the above-described determination resultchanges from “1” to “0”, and outputs “F=0” to the circuit 1116 as atrailing section when changing from “−1” to “0”. Here, for example, whenthe mark length detection circuit 1115 performs mark length detection ina time zone k2 to k3 of a differential signal as shown in (A) of FIG.28, a record mark length (pattern interval) P as shown in (B) of FIG. 28can be obtained. Moreover, (C) of FIG. 28 shows the change direction F.

The correction amount generation circuit 1116 generates a correctionamount by the following formula (9) based on the signal supplied fromthe mark length detection circuit 1115.Y(i)=−A·P(i−1)+B·P(i)  (9)A and B are the predetermined correction coefficients set beforehand,P(i) is the record mark length at present time unit, and P(i−1) denotesthe record mark length at one previous time unit. That is, the presentrecord mark length and the record mark length at one previous time unitare multiplied by the predetermined correction coefficient,respectively, and the correction amount is computed by adding thevalues.

Here, in magneto-optical recording, the temperature of a laser beamirradiation section of a magneto-optical recording medium reaches to aCurie point by irradiation of a laser beam at the time of record, andmagnetization disappears. However, at the peripheral section wheretemperature is not rising to a Curie point, magnetization exists and astray magnetic field caused by the magnetization exists. Although amagnetic domain wall which is a record mark edge is formed in a rearedge in the light beam traveling direction, those stray magnetic fieldsact in the state that they are superimposed on the modulation magneticfield applied by the magnetic head from the outside for magnetic domainwall formation, at the time of the magnetic domain wall formation whichis a record mark edge. The size of this stray magnetic field changeswith the interval between a magnetic domain wall formed immediatelybefore and a magnetic domain wall which is going to be formed next,i.e., the record mark length to be formed, and the mark length locatedin front of it. Therefore, the intensity of a stray magnetic field thatacts on a magnetic domain wall forming section changes with a marklength (or mark length row) to be recorded.

In addition, the formed location of a magnetic domain wall is determinedin the relation between temperature and magnetic field strength. Here,since the laser beam intensity and the magnetic field strength appliedfrom the magnetic head are kept in a steady state and the stray magneticfield intensity that is superimposed differs if a record mark length ora record mark length row differs, the magnetic field strength applied toa location of magnetic domain formation is stray magnetic fieldintensity in addition to the magnetic field strength from the magnetichead. Hence, the magnetic field strength substantially applied to amagnetic domain forming part changes with the record mark length orrecord mark length row to be formed. In consequence, a phenomenon that alocation of magnetic domain wall formation is changed by record marklength appears.

In this embodiment, a waveform deviation occurring depending on therecord mark length based on such a phenomenon is corrected. That is, asshown in Formula (9), the record mark length at one previous time unitand the record mark length at present time unit are multiplied by thepredetermined correction coefficients, respectively, at the time ofinformation reproduction, addition of their values is computed as thecorrection amount, and the waveform deviation of the reproduced signalis corrected on the basis of this correction amount. In addition, as forthe correction coefficients A and B in Formula (9), it is desirable toobtain them beforehand by an experiment, for example, it may be readafter it was recorded beforehand on a control truck of a disk at thetime of shipment of a recording medium, or it may be read after it waswritten in ROM of an apparatus.

The waveform correction circuit 1111 delays an RF digital signalsupplied from the A/D converter 1110, and corrects the RF digital signalbased on the correction amount Y and a signal F showing the direction ofa change, obtained from the correction amount generation circuit 1116.The outline of the correction is shown in FIGS. 29A to 29C. FIG. 29Ashows a waveform of a reproduced signal, and a black circle ● denotes asampling point. In addition, a broken line in FIG. 29A is a waveformafter correction, and each asterisk *- shows a sampling point after thecorrection. FIG. 29B shows a differential signal before correction, andFIG. 29C shows a differential signal after the correction.

The waveform correction circuit 1111 computes an offset amount S ofsignal amplitude based on the correction amount Y, subtracts the offsetamount S near a changing point when the changing direction F is “1”(when the reproduced signal falls), and adds the offset amount S near achanging point when the changing direction F is “0” (when the reproducedsignal rises). The offset amount S is obtained from S=K·Y(i). Inaddition, k is a coefficient. The corrected RF digital signal issupplied to the decoder circuit 1112. Here, the decoder circuit 1112performs decoding by differential detection.

FIG. 30A shows a differential signal with respect to the corrected RFdigital signal, and FIG. 30B shows decoded data. In the differentialdetection, “1” is outputted when a differential signal is equal to orlarger than the positive threshold T1, “0” is outputted when equal to orless than the negative threshold T2, and in other cases a value that isthe same as that of decoded data at one previous time unit is outputted.It is possible to reduce a decoding error by a waveform deviation byperforming such correction.

Next, the specific reproduction operation of this embodiment will beexplained on the basis of FIGS. 31A to 31H. FIG. 31A shows an RF digitalsignal, FIG. 31B shows a clock, FIG. 31C shows a differential signal,FIG. 31D shows a mark length, FIG. 31E shows a change direction, FIG.31F shows a gate of setting a correction zone, FIG. 31G shows acorrection offset amount, FIG. 31H shows a digital signal aftercorrection. Here, when a light beam for reproduction is radiated fromthe optical head 1104 on the magneto-optical disk 1101 which isrotating, the reflected light from the magneto-optical disk 1101 isdetected by the optical head 1104 and a reproduced signal is generated,and the reproduced signal is supplied to the A/D converter 1110 througha preamplifier 1105 and an AGC circuit 1109. The A/D converter 1110, asshown in FIG. 31A, outputs an RF digital signal with synchronizing withthe clock in FIG. 31B, and supplies the RF digital signal to the marklength detection circuit 1115.

The mark length detection circuit 1115 generates a differential signalas shown in FIG. 31C, and simultaneously computes the record mark lengthP on the basis of the counter value synchronized with the clock in FIG.31B. Furthermore, the mark length detection circuit 1115 detects thechange direction of leading and trailing edges from the differentialsignal in FIG. 31C, and outputs 0→1 as the change direction of thedifferential signal 1→0 or outputs 1→0 as the change direction of thedifferential signal −1→0, as shown in FIG. 31E.

The correction amount generation circuit 1116 computes a correctionamount by Formula (9) based on the record mark length P in FIG. 31D,further converts it into the offset amount S of amplitude, and outputsthe offset amount S as shown in FIG. 31G. The waveform correctioncircuit 1111 gives predetermined delay to the RF digital signal obtainedfrom the A/D converter 1110, as shown in FIG. 31F, internally generatesa correction gate, which controls a section where the RF digital signalis corrected on the basis of the signal from the correction amountgeneration circuit 1116, and subtracts or adds an offset from or to theamplitude of the RF digital signal in this correction gate section,respectively. That is, the waveform correction circuit 1111 creates acorrection gate signal, which is shown in FIG. 31F with corresponding toan edge section of the RF digital signal, and performs addition orsubtraction of an offset in the section where this correction gatesignal is “1”. Thereby, since the reproduced signal shown by a brokenline is corrected into the reproduced signal shown by a solid line asshown in FIG. 31H, the waveform deviation can be corrected.

Embodiment 6

Next, a sixth embodiment of the present invention will be explained. Thesixth embodiment adaptively generates the above-mentioned correctioncoefficient from a reproduced signal, and flexibly corresponds to afluctuation of the correction coefficient due to the individualdifference of a medium. In addition, waveform correction is alsoperformed with a method different from that in the sixth embodiment.FIG. 32 is a block diagram showing a second embodiment of the presentinvention. In addition, the explanation of the same portions as those inFIG. 25 will be omitted with assigning the same numerals as those havingthe same configuration and performing the same operation.

In FIG. 32, a correction coefficient generation circuit 1152 adaptivelygenerates correction coefficients A and B in Formula (9). In addition, areproduction compensating circuit 1150 generates a correction amount Ybased on the record mark length generated by the mark length detectioncircuit 1115, and supplies it to a waveform correction circuit 1153.Here, the correction amount generation circuit 1151 generates acorrection amount by using the correction coefficients A and B that aregenerated in the correction coefficient generation circuit 1152. Thewaveform correction circuit 1153 corrects and outputs the sampled datanear an edge section based on the correction amount Y supplied from thecorrection amount generation circuit 1151.

Next, the configuration and operation of each of the above-describedunits will be described. FIG. 33 is a block diagram showing theconfiguration of a correction coefficient generation circuit 1152. InFIG. 33, a reference area detection unit 1901 detects the area where thepredetermined record mark row for generating a correction coefficient isrecorded, and starts the sequence for generation of a correctioncoefficient. The record mark row shall be recorded on the predeterminedarea set beforehand.

When a correction coefficient is generated, an RF digital signalcontrolled and reproduced so that the signal in a predetermined addressmay be reproduced by a CPU not shown in the drawings or the like issupplied to the reference area detection unit 1901 through the A/Dconverter 1110. When detecting a predetermined record mark row from theRF digital signal, the reference area detection unit 1901 startsgeneration processing of the correction coefficient. As for thedetection of a record mark row, it is possible to use well-known methodssuch as the above-mentioned differential detection and PRML.

The jitter detection unit 1902 computes a jitter by reproducing apredetermined record mark row, and generates a correction coefficientbased on this. The operation of the jitter detection unit 1902 will bedescribed with FIG. 34. In FIG. 34, black circles ● and open circles ∘are sampling points of a reproduced signal 1910 with a PLL clock. Thejitter detection unit 1902 acquires sampled data in an edge section as aphase error signal based on the signal from the reference area detectionunit 1901, and detects a jitter based on this sampled data.

Next, the operation of jitter detection will be described on the basisof FIGS. 35A to 35D. FIG. 35A shows a reproduced signal (signal pattern)for the jitter detection, FIG. 35B shows a PLL clock, FIG. 35C shows adifferential signal of the reproduced signal, and FIG. 35D shows a phaseerror signal obtained from the sampled data at points of open circle ∘shown in FIG. 34. The jitter detection unit 1902 detects leading andtrailing edges of a signal pattern shown in FIG. 35A by the differentialsignal in FIG. 35C, and as shown in FIG. 34, generates a phase errorsignal (D) from the gate section generated based on the differentialsignal.

Subsequently, the jitter detection unit 1902 selects the phase errorsignal obtained with the combination of a further specific record markrow out of the generated phase error signal, and generates a jittersignal. For example, in the predetermined record mark row of 8T-2T-2T-8Tas shown in FIG. 35A, phase error signals J3 and J4 obtained in an edgesection of a 2T pattern after 8T are selected. Since detection of asignal pattern is performed in the above-mentioned reference areadetection unit 1901, an 8T-2T pattern can be obtained from the detectionresult.

The jitter detection can be performed from addition of the phase errorsignals J3 and J4 in trailing and leading sections of the 2T pattern, asshown in FIG. 36. The added value of J3 and J4 becomes “0” when there isno waveform deviation, but when the length of the 2T pattern isfluctuated by the waveform deviation, the added value fluctuates betweenplus and minus sides. The jitter detection unit 1902 generates a jittersignal in a specific pattern from a predetermined record mark row asshown in the above-described example, and computes an average value.

The correction coefficient calculation unit 1903 computes correctioncoefficients in Formula (1) from the generated jitter signal. Here, thecorrection coefficients A and B are obtained by Formula (10) with afunction K showing the relation of (jitter signal)−(correctioncoefficient) which is beforehand obtained from the characteristics of amedium, etc.Correction coefficient A=K _(A)(Jt), B=K _(B)(Jt)  (10)

Jt is a jitter signal obtained in the jitter detection unit 1902. Inaddition, it may be also possible to obtain an effect of the same extenteven if correction coefficients A and B are equal to each other inFormula (9), and in that case, it is also possible to compute only thecorrection coefficient A in Formula (10), and to reduce the load ofprocessing. The generated correction coefficient is supplied to thecorrection amount generation circuit 1151 in the reproductioncompensating circuit 1150.

FIG. 37 shows the outline of waveform correction in the sixthembodiment. The interpolation of a signal realizes the correction of awaveform in this embodiment. FIG. 37 shows a signal near an edge of areproduced signal. A broken line is a waveform of the reproduced signal,black circles ● are sampling points of the digital signal sampled withthe PLL clock, and a waveform deviation is generated by a medium'scharacteristics, etc. The correction amount generation circuit 1151computes a correction amount Y based on the correction coefficientsobtained by the correction coefficient generation circuit 1152. Inaddition, although a correction amount Y can be obtained by Formula (9),Formula (11) can be also substituted in simple as A=0 in Formula (9).Y(i)=B·P(i)  (11)Here, the correction amount Y is computed by Formula (11), and aninterpolation coefficient G as shown in FIG. 37 is generated on thebasis of this. It becomes unnecessary to provide memory holding twoadjacent record mark lengths P(i) and P(i−1) by using Formula (11), andit is possible to reduce the load of operation. The waveform correctioncircuit 1153 computes sampled data E2′ and E3′ (shown by black squares▪) which are corrected by linear interpolation from the sampled data E1to E3 in an edge section and the interpolation coefficient G. Forexample, E2′ can be obtained by the following Formula (12).E2′=(G/T)·E1+((T−G)/T)·E2  (12)T denotes an interval between sampling clocks. In addition, although thecase of linear interpolation is shown here, it is also possible tosubstitute other well-known interpolation methods for this. Thereby,since the edge shift by a waveform deviation can be reduced, a factor ofa decode error is eliminated and it becomes possible to aim atimprovement in recording density.

In addition, although the waveform correction here is performed withrespect to a reproduced digital signal, the same effect can be obtainedby correcting a differential signal when decoding by the differentialdetection. In addition, when decoding by PRML, there is no need to saythat it is also possible to perform correction with respect to awaveform given PR equalization.

Embodiment 7

Next, a seventh embodiment of the present invention will be explained.In this embodiment, the following formula is used as a calculationformula of the correction amount Y in the correction amount generationcircuit 1116 in FIG. 25.Y(i)=−A·(P(i−1)−R)+B·(P(i)−R)  (13)Here, R denotes a mark length that becomes a reference. It is possibleto reduce an absolute value of a correction amount by generating thecorrection amount by Formula (13). For example, the correction amountbecomes “0” by making R=2 in Formula (13) when the record mark length is2T. Thereby, since the fluctuation of a signal due to correction can bedistributed to plus and minus sides, a change from the originalreproduced signal can be suppressed.

Embodiment 8

Next, an eighth embodiment of the present invention will be explained.FIG. 38 is a block diagram showing the configuration of the eighthembodiment of the present invention. In FIG. 38, a data PLL 1154 isadded to the configuration in FIG. 25. Others are similar to those inFIG. 25. The data PLL 1154 generates a clock signal based on thereproduced signal whose a waveform deviation is corrected in thewaveform correction circuit 1111 by the same method as that in the fifthembodiment.

FIG. 39 is a block diagram showing the configuration of the data PLL1154. In this figure, a phase error detection unit 1301 detects a phaseerror based on sampled data in a leading edge section of a reproducedsignal. A loop filter 1302 performs removal of unnecessary noise fromand reduction compensation of a phase error signal. A VCO 1303 generatesa clock signal with a frequency corresponding to a control voltage. Thedata PLL detects a phase error from an edge section of the reproducedsignal that is corrected, and supplies the detected signal as a controlsignal of the VCO after filtering. It is possible to obtain the clocksynchronizing with the reproduced signal by performing the loop of thisdetected signal.

In the apparatus of this embodiment, since a phase error is detectedfrom the reproductive signal whose waveform deviation is corrected, theinfluence of incorrect detection as shown in FIG. 42D can be reduced,and a proper reproduced signal can be obtained. In addition, a detectionmethod of a phase error is not limited to the above-described method,but another well-known technology can be used.

1. An optical information reproducing method of detecting a reproducedsignal on a basis of a record mark formed in an optical informationrecording medium and decoding record data on a basis of the reproducedsignal, comprising the steps of: decoding a record data on a basis ofthe reproduced signal; detecting a mark length of each record mark on abasis of the reproduced signal; and correcting a waveform of thereproduced signal before the decoding by a correction amountcorresponding to the detected mark length at the time of informationreproducing.
 2. The optical information reproducing method according toclaim 1, wherein the correction is performed by performing addition orsubtraction of an offset amount according to the correction amount withrespect to the reproduced signal.
 3. The optical information reproducingmethod according to claim 1, wherein the correction is performed byinterpolating the reproduced signal with an interpolation coefficientcorresponding to the correction amount.
 4. The optical informationreproducing method according to claim 1, wherein the correction amountis computed on basis of a measurement value obtained by measuring aphase or amplitude displacement of a reproduced signal obtained when aspecific record mark length is reproduced.
 5. The optical informationreproducing method according to claim 1, wherein the optical informationrecording medium is a magnetic domain wall movement-type magneto-opticalrecording medium.
 6. The optical information reproducing methodaccording to claim 1, wherein the correction amount is an amount thatcompensates fluctuation of a record mark edge by a stray magnetic field.7-9. (canceled)
 10. The optical information reproducing method accordingto claim 6, wherein the correction amount is held in a table for everycombination of n(k) and n(k+1), wherein n(k) is a mark length at oneprevious time unit, and n(k+1) is a mark length at present time unit.11-15. (canceled)
 16. The optical information reproducing methodaccording to claim 6, wherein the correction amount is computed on basisof a measurement value obtained by measuring a jitter of a reproducedsignal obtained when user data recorded on the medium is reproduced. 17.The optical information reproducing method according to claim 16,wherein the jitter is measured on a basis of amplitude or an phase errorof the reproduced signal.
 18. An optical information reproducingapparatus for detecting a reproduced signal on a basis of a record markformed in an optical information recording medium and decoding a recorddata on a basis of a reproduced signal, comprising: a decoder circuitfor decoding a record data on a basis of a reproduced signal; adetection circuit for detecting a mark length of each record mark on abasis of the reproduced signal; and a correction circuit for correctinga waveform of the reproduced signal before the decoding by a correctionamount corresponding to the detected mark length at the time ofinformation reproducing.
 19. The optical information reproducingapparatus according to claim 18, wherein the correction circuit performsthe correction by performing addition or subtraction of an offset amountaccording to the correction amount with respect to the reproducedsignal.
 20. The optical information reproducing apparatus according toclaim 18, wherein the correction circuit performs the correction byinterpolating the reproduced signal with an interpolation coefficientcorresponding to the correction amount.
 21. The optical informationreproducing apparatus according to claim 18, further comprising acircuit for generating the correction amount, wherein the correctionamount generation circuit measures a phase or amplitude displacement ofa reproduced signal obtained when a specific record mark length isreproduced, and computes the correction amount on basis of themeasurement value. 22-24. (canceled)
 25. The optical informationreproducing apparatus according to claim 21, wherein the correctionamount generation circuit is held in a table for every combination ofn(k) and n(k+1), wherein n(k) is a mark length at one previous timeunit, and n(k+1) is a mark length at present time unit.
 26. (canceled)27. The optical information reproducing method according to claim 1,wherein the decoding is performed by differential detection and thereproduced signal before the decoding also includes a differentialsignal used in the differential detection.
 28. The optical informationreproducing method according to claim 1, wherein the decoding isperformed by PRML and the reproduced signal before the decoding alsoincludes a signal equalized with PR waveform.